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Even as global health experts were nervously eyeing a new coronavirus that has caused more than 10 deaths, word has arrived that China may be facing a new threat from an influenza virus typically limited to birds. Currently, there have been nine confirmed infections that resulted in three deaths. However, there may be other infections that haven't come to the attention of health authorities, and the original source of the infections remains unknown.

This particular strain is called H7N9 (for more on the H/N nomenclature, see our influenza primer). It's typically confined to birds, although CNN notes that H7N9 has infected humans a number of times in the past. Those infections, however, have rarely resulted in deaths. According to the Associated Press, Chinese health authorities say this virus is infecting birds without causing obvious symptoms, making it harder to track than past avian flu outbreaks, notably the H5N1 flu.

The World Health Organization's FAQ on the outbreak indicates that there is no evidence so far that the virus can spread among humans. That said, there are a couple of worrying indications. Chinese health authorities have published the DNA sequence of the virus, and one flu expert contacted by the Canadian Press notes that some of the genetic differences between this H7N9 strain and other avian influenza viruses could be an indication that this virus has adapted to mammals. A different report from the Associated Press says that an individual who died from the virus had two children who also came down with severe respiratory illnesses.

Two other facts seem pertinent to the virus' spread. Of the individuals who have contracted it so far, only one is involved in the poultry industry. And Chinese health authorities have started testing some of the bodies of pigs that have been found in a river that feeds the local water supply. So far, the virus wasn't present in any of the ones tested.

To summarize what we know: not a lot. Although H7N9 is an avian influenza virus, it can be present in bird populations without causing any symptoms, making it difficult to even identify which populations to be screening. This particular virus may be partly adapted to mammalian growth as well, which opens up other options for its spread. So far, however, there's no indication that the mammal doing the spreading is a human.

To complicate matters further, the full extent of flu viruses within a human population are often difficult to track. If 90 percent of the people who carry it only end up with minor flu symptoms, they probably won't come to the attention of medical authorities. (This often inflates the initial fatality rates, which tend to drop once widespread testing reveals a lot of additional cases that weren't initially recognized as being anything out of the ordinary.) And new cases tend to occur amid a background of infections caused by the typical mammalian flu viruses.

At this point, there have been enough worrying signs that the Chinese medical establishment is undoubtedly engaged in widespread screening for the virus. The country as a whole is heavily invested in genomics and has past experiences with dealing with emerging viral risks. But it may take weeks for that testing to provide a clearer picture of where the virus originated and how it's spreading to humans. Until we have a clearer sense of that, the overall risk is hard to evaluate. We'll provide updates should any new information warrant it.

"However, there may be other infections that haven't come to the attention of health authorities, and the original source of the infections remains unknown."

Even in the west surveillance isn't going to pick up every infection, and this is doubly so in China. There may be hundreds, thousands of infections. We saw the same sort of thing with early death rates in previous scares. Once the virus was "in the wild" it was no more deadly than the normal flu.

It's hard to give an exact frequency of occurrence, as it probably happens without noticeable effect most of the time, but the mechanism of species hopping isn't difficult. The virus particles are coated with proteins which recognize and bind to proteins found specifically in birds, or pigs, or humans, and allow the virus to infect that species. Ridiculous numbers of viruses are produced from a single cell that's infected, and a significant proportion will have mutations, including in the protein that infects an animal. If it just happens to be different enough to infect that animal, then you can get a spread from pig to human, for example. Things get even worse when you get infections of two different flu viruses in the same animal.

Why always China? I have theories, but I'm inclined to listen to others.

I think proximity is the biggest factor, and I assume there are just many more Chinese people who basically live in the same room as their chickens, pigs, et cetera.

Maybe by that measure you would expect India to be the same, but India is a lot hotter so maybe they are more likely to keep their animals outside. I stayed with a family in Nepal once and the house was just one large room for all the people and a few animals.

Maybe I'm wrong, but I don't think they have particularly more strains of flu in their chickens and pigs, just it jumps to humans more often.

Can someone explain to me why these things are news? "A virus mutated, oooooh!" And? Read a neat paper a while ago suggesting any "we're all going to die!" virus would essentially burn itself out, causing deaths faster than it could spread. And none of these viruses are ever even suggested to be some sort of worst case scenario even then.

So until the zombie plague springs up, why do we need to know if some avian strain jumps to humans?

Flu vaccines are only useful if they manage to pick the right strains that year. Something emergent like this won't be in the vaccine, so a vaccine won't help. If it ends up being very serious and spreads slowly enough for them to come up with a vaccine, then they can be useful. Of course, the whole issue with pandemics is that they sneak up on you and spread quickly.

Read a neat paper a while ago suggesting any "we're all going to die!" virus would essentially burn itself out, causing deaths faster than it could spread.

They will, unless they don't. With modern travel a contagion doesn't have to be contagious but asymptomatic all that long to get spread worldwide. A day or two of being able to spread it around would be enough to cause serious problems. It doesn't help that people's first instinct in this kind of situation is to run away from the infection hotspots, which can just end up spreading it faster. The reason people have an itchy trigger finger is that the only way to contain a serious outbreak is swift quarantine and travel shutdowns. If something that has a high mortality rate gets out in the world, there is not going to be a lot that we can do to stop it.

If you look at the history of vaccinations, it was noticed in the late 18th century that milkmaids didn't appear to get smallpox. It was discovered that milkmaids who had previously caught cowpox by continually pulling an infected cow's udder were immune to smallpox.

The point of my story is that there's a difference between a virus hopping onto us and infecting us, as a virus hopping onto us, then hopping from person to person causing mass casualties.

The virus either might not spread very well, and die out. Or it might kill everyone who gets it before it can spread very far, and die out.

It's like asking how often do cat fleas hop onto us: all the time. How often do people get cat fleas: not often, if ever.

I'm no scientist but I think it's not that uncommon: flies, ticks, mosquitos, rats, dogs, pigs, skeevers... oh, wait, sorry, wrong reality... One species can simply carry the disease without being much affected itself.

It doesn't help that people's first instinct in this kind of situation is to run away from the infection hotspots, which can just end up spreading it faster.

Interesting factoid from an Islam class I took long ago: the idea of quarantine is part of Islam, included as a hadith (saying of the Prophet):

"Abd ar-Rahman ibn Awf told him that the Messenger of Allah, may Allah bless him and grant him peace, said, "If you hear that a land has a plague in it, do not go forward to it. If it comes upon a land which you are in, do not depart in flight from it."http://ahadith.co.uk/permalink-hadith-4677

Read a neat paper a while ago suggesting any "we're all going to die!" virus would essentially burn itself out, causing deaths faster than it could spread. And none of these viruses are ever even suggested to be some sort of worst case scenario even then.

The 1918 influenza outbreak had about a 20% death rate, once infected. Roughly 5% of the world population died.

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why do we need to know if some avian strain jumps to humans?

Apparently YOU don't need to know, and wouldn't care anyway. Why did you even bother reading this article?

Very passing refrence to the 16,000 rotting pig carcasses, and a few thousand duck, that 'mysteriously' showed up in a river near Shanghai last month, i'd be very intersted if a conectin surfaces.Pigs and chickens are almost certaincy gonna be a problem for us. The ( slightly racist?) comment about chinese living in the same room as them misses the basic fact that in china, as here, pigs and chickens are massively factory farmed. Large monocultures of mostly closely related, if not extremely inbred, animals living it tight cramped conditions most likley pumped full of prophylactic antibiotics to increase growth rates are excellent fertile fields for new significant epidemics to get started. Then if you mix a population with endemic deseases that could possiblely jump the species line to a organism that has not developed an acomidation to it, well hell ... Tons of fun,. From little things Sometimes big results, There are theories that link the black death to minor floods in central asia that drove marmots out of certain valleys and eventually devasted the population of europe, and that was at the speed of sail.Then again the black death did wonders for europe's economy when it was over, nothing to better raise the value of labour than killing almost everyone, and it and all the other plagues gave the europians a particularly nasty hidden weapon for thier colonization of the americas ...

Why always China? I have theories, but I'm inclined to listen to others.

Because China is a shithole. Be it 20.000 dead pigs floating down a river, air so polluted that you can cut it with a knife, fire-extinguishers installed every few meters on Tiananmen Square to prevent self-immolation, China has it all!

Why always China? I have theories, but I'm inclined to listen to others.

I think it's a given that more populace areas tend to have more of these kinds of outbreak as well as the kind of cultural norms tend to give rise to cross-species contamination (as pointed out). It's a numbers game, a statistical calculation. It's not like Mother Nature gives a rats ass on where you live, what religion you pray to or the color of your skin.

Very passing refrence to the 16,000 rotting pig carcasses, and a few thousand duck, that 'mysteriously' showed up in a river near Shanghai last month, i'd be very intersted if a conectin surfaces.Pigs and chickens are almost certaincy gonna be a problem for us. The ( slightly racist?) comment about chinese living in the same room as them misses the basic fact that in china, as here, pigs and chickens are massively factory farmed. Large monocultures of mostly closely related, if not extremely inbred, animals living it tight cramped conditions most likley pumped full of prophylactic antibiotics to increase growth rates are excellent fertile fields for new significant epidemics to get started. Then if you mix a population with endemic deseases that could possiblely jump the species line to a organism that has not developed an acomidation to it, well hell ... Tons of fun,. From little things Sometimes big results, There are theories that link the black death to minor floods in central asia that drove marmots out of certain valleys and eventually devasted the population of europe, and that was at the speed of sail.Then again the black death did wonders for europe's economy when it was over, nothing to better raise the value of labour than killing almost everyone, and it and all the other plagues gave the europians a particularly nasty hidden weapon for thier colonization of the americas ...

I'm sorry, was in no way trying to be racist, it's a simple fact that many people in the developing world live in the same room as their animals, as was common in Europe until relatively recently, and as I testified from my personal experience (the family in Nepal were lovely, by the way).

I think I'm right in saying that of China's population of approximately 1.2 billion people, roughly 50% still work the land (I can find the reference somewhere). That's a lot of people who still literally live "cheek by jowl".

Most of the terrible diseases which have 'plagued' mankind through the ages have spread to us from domestic animals; and it's not from shagging monkeys, it's because for most of our history we have lived with them.

I would be interested to hear if modern farming practises actually make disease outbreaks worse. I would have thought that monitoring is much better and once a disease has ripped through a population it would die out again quicker, rather than lingering in semi-isolated pockets. Certainly the antibiotic overuse you hint at is not going to do much about flu, which is a virus.

You raise an interesting point about European diseases being nasty news for the Americas though. Has it ever occurred to you why they didn't have many nasty diseases waiting for the Europeans? You may want to think about how few farmed animals are indigenous to the Americas, that the aboriginal people may have lived with and caught diseases from.